Apparatus and method for enhancing laser beam efficacy in a liquid medium

ABSTRACT

The present disclosure generally relates to the field of laser based medical devices. Particularly, but not exclusively, the present disclosure relates to an apparatus and method for enhancing laser beam efficacy in a liquid medium. In many embodiments, laser pulses are modulated based on bubble dynamics to improve energy delivery to a target. A variety of exemplary pulse modulation scheme are described including modulating pulse power down during expansion of an index bubble and modulating pulse power up during collapse of the index bubble.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 toU.S. Provisional Patent Application No. 63/118,117, titled “Apparatusand Method for Enhancing Laser Beam Efficacy in a Liquid Medium”, filedon Nov. 25, 2020, the entirety of which is incorporated herein byreference.

This application claims the benefit of priority under 35 U.S.C. § 119 toU.S. Provisional Application No. 63/118,857, titled “Method and Systemfor Estimating Distance Between a Fiber End and a Target”, filed on Nov.27, 2020, the entirety of which is incorporated herein by reference.

This application claims the benefit of priority under 35 U.S.C. § 119 toU.S. Provisional Patent Application No. 63/252,830, titled “Method andSystem for Estimating Distance Between a Fiber End and a Target”, filedon Oct. 6, 2021, the entirety of which is incorporated herein byreference.

TECHNICAL FIELD

The present disclosure generally relates to the field of laser basedmedical devices. Particularly, but not exclusively, the presentdisclosure relates to an apparatus and method for enhancing laser beamefficacy in a liquid medium.

BACKGROUND

Lasers are widely used for performing various medical treatments such astissue coagulation, ablation, cutting, fragmenting, dusting andenucleation. Laser treatments are conducted through and within variousmediums and environments such as gases, solids, and liquids. Duringlaser treatments, the interaction between the laser radiation and atarget object (e.g., body tissue such as prostate, kidney, or urinarystones), depends on the laser used and, among other things, on theabsorption, reflection, and dispersion of the environment and the targetobject. Ureteral stones, kidney stones, or prostate are only threeexamples of common targets which may be treated by a laser. Typically,the treatment environment may be saline or other similar liquids. Theefficiency of laser treatment may be a function of the interactionbetween the laser energy and target. The portion of the laser energythat reaches and is absorbed by the target contributes to the requiredsurgical effect. However, the laser energy absorbed by the environmentmedium can be considered lost energy, which is no longer available fortarget treatment. Oftentimes, laser parameters, such as wavelength, maybe selected based on the desired clinical effect and the characteristicsof the target. For example, infrared (IR) lasers, such as Holmium orThulium, may be used for laser lithotripsy to treat ureteral stones,renal colic and for prostate ablation or enucleation.

BRIEF SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to necessarily identify keyfeatures or essential features of the claimed subject matter, nor is itintended as an aid in determining the scope of the claimed subjectmatter.

In one aspect, the present disclosure relates to a system, comprising afiber laser and a controller. The controller may include a processor andmemory. The memory may include instructions that when executed by theprocessor cause the processor to perform one or more of: determine apulse energy for the fiber laser; identify a distance between a tip ofthe fiber laser and a target, wherein a liquid is located between thetip of the fiber laser and the target; determine a modulation schemebased on the distance; set an initial pulse power for the modulationscheme to generate an index bubble in the liquid based on the distance;and initiate a pulse according to the modulation scheme via the fiberlaser, wherein the modulation scheme reduces power of the pulse afterinitiation of the pulse at the initial pulse power.

In some embodiments, the modulation scheme increases power of the pulseto a maximal system power level at a time estimated for the index bubbleto reach maximal size. In some such embodiments, the instructions, whenexecuted by the processor, further cause the processor to estimate thetime the index bubble takes to reach maximal size based on the initialpulse power and an absorption coefficient of the liquid at a wavelengthof the fiber laser.

In various embodiments, the instructions, when executed by theprocessor, further cause the processor to identify an updated distancebetween the tip of the fiber laser and the target; and determine anupdated modulation scheme based on the updated distance.

In several embodiments, the modulation scheme is configured to modulatepulse power down during expansion of the index bubble and modulate pulsepower up during collapse of the index bubble.

In many embodiments, the modulation scheme comprises an initialmodulation frequency and the instructions, when executed by theprocessor, further cause the processor to determine the initialmodulation frequency based on a time to collapse of the index bubble, atime for the index bubble to reach maximum size, and a time from lasinginitiation to start of bubble formation.

In some embodiments, the instructions, when executed by the processor,further cause the processor to set the initial pulse power for themodulation scheme to generate the index bubble in the liquid based onthe distance and the pulse energy.

In various embodiments, the instructions, when executed by theprocessor, further cause the processor to integrate the power of thepulse with respect to time and terminate the pulse when the integral ofthe power of the pulse with respect to time equals the pulse energy.

In several embodiments, the instructions, when executed by theprocessor, further cause the processor to classify the target as distanttarget based on the distance and set the initial pulse power to amaximal system power level based on classification of the target asdistant. In several such embodiments, the modulation scheme isconfigured obtain a resonant effect by cycling at periods between 0.7and 1.3 times a time from start to collapse of the index bubble.

In another aspect, the present disclosure relates to at least onenon-transitory computer-readable medium comprising a set of instructionsthat, in response to being executed by a processor circuit, cause theprocessor circuit to perform one or more of: determine a pulse energyfor a fiber laser; identify a distance between a tip of the fiber laserand a target, wherein a liquid is located between the tip of the fiberlaser and the target; determine a modulation scheme based on thedistance; set an initial pulse power for the modulation scheme togenerate an index bubble in the liquid based on the distance; andinitiate a pulse according to the modulation scheme via the fiber laser,wherein the modulation scheme reduces power of the pulse afterinitiation of the pulse at the initial pulse power.

In some embodiments, the modulation scheme increases power of the pulseto a maximal system power level at a time estimated for the index bubbleto reach maximal size. In some such embodiments, the set ofinstructions, in response to execution by the processor circuit, furthercause the processor circuit to estimate the time the index bubble takesto reach maximal size based on the initial pulse power and an absorptioncoefficient of the liquid at a wavelength of the fiber laser.

In various embodiments, the set of instructions, in response toexecution by the processor circuit, further cause the processor circuitto: identify an updated distance between the tip of the fiber laser andthe target; and determine an updated modulation scheme based on theupdated distance.

In several embodiments, the set of instructions, in response toexecution by the processor circuit, further cause the processor circuitto set the initial pulse power for the modulation scheme to generate theindex bubble in the liquid based on the distance and the pulse energy.

In many embodiments, the set of instructions, in response to executionby the processor circuit, further cause the processor circuit tointegrate the power of the pulse with respect to time and terminate thepulse when the integral of the power of the pulse with respect to timeequals the pulse energy.

In yet another aspect, the present disclosure may include a methodcomprising one or more of determining a pulse energy for a fiber laser;identifying a distance between a tip of the fiber laser and a target,wherein a liquid is located between the tip of the fiber laser and thetarget; determining a modulation scheme based on the distance; settingan initial pulse power for the modulation scheme to generate an indexbubble in the liquid based on the distance; and initiating a pulseaccording to the modulation scheme via the fiber laser, wherein themodulation scheme reduces power of the pulse after initiation of thepulse at the initial pulse power.

In some embodiments, the method includes modulating pulse power downduring expansion of the index bubble and modulating pulse power upduring collapse of the index bubble.

In various embodiments, the method includes classifying the target asdistant target based on the distance and set the initial pulse power toa maximal system power level based on classification of the target asdistant. In various such embodiments, the method includes cycling atperiods between 0.7 and 1.3 times a time from start to collapse of theindex bubble.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present disclosure are described by wayof example with reference to the accompanying figures, which areschematic and not intended to be drawn to scale. In the figures, eachidentical or nearly identical component illustrated is typicallyrepresented by a single numeral. In will be appreciated that variousfigures included in this disclosure may omit some components, illustrateportions of some components, and/or present some components astransparent to facilitate illustration and description of componentsthat may otherwise appear hidden. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment shown where illustration is not necessary to allow those ofordinary skill in the art to understand the disclosure. In the figures:

FIG. 1 illustrates an exemplary diagram of pulses of a Holmium laser anda Thulium laser according to one or more embodiments described herein.

FIGS. 2A and 2B illustrate various aspects of Holmium laser short pulsesin different mediums according to one or more embodiments describedherein.

FIGS. 3A and 3B illustrate various aspects of Thulium laser long pulsesin different mediums according to one or more embodiments describedherein.

FIG. 4A illustrates an exemplary diagram of a Thulium laser long pulsein an air medium according to one or more embodiments described herein.

FIG. 4B illustrates an exemplary diagram of a Thulium laser long pulsein a liquid medium according to one or more embodiments describedherein.

FIG. 5 illustrates an exemplary time series of images of bubble dynamicsaccording to one or more embodiments described herein.

FIG. 6 illustrates an exemplary diagram of laser power modulated inrelation to bubble size according to one or more embodiments describedherein.

FIG. 7 illustrates an exemplary diagram of modulated and unmodulatedlaser pulses in conjunction with associated bubble dynamics according toone or more embodiments described herein.

FIG. 8 illustrates an exemplary diagram of a modulated laser pulse inconjunction with associated bubble dynamics according to one or moreembodiments described herein.

FIG. 9 illustrates an exemplary laser system according to one or moreembodiments described herein

FIG. 10 illustrates an exemplary process flow according to one or moreembodiments described herein.

FIG. 11 illustrates a block diagram of a method for implementingembodiments consistent with the present disclosure.

FIG. 12 illustrates a block diagram of an exemplary computer system forimplementing embodiments consistent with the present disclosure.

DETAILED DESCRIPTION

The present disclosure provides medical devices and techniques forenhancing laser beam efficacy in a liquid medium, such as for a desiredsurgical effect on a target. The liquid environment of many treatmentenvironments tends to absorb a significant portion of laser energy. Forexample, the liquid medium can absorb and attenuate the laser energy,leaving less energy available for the desired surgical effect on thetarget. Additionally, energy absorbed by the liquid medium can heatsurrounding tissue, leading to unwanted safety issues and the need toirrigate the areas with cooling fluids.

One laser treatment technique, referred herein as the bubble patheffect, utilizes one or more bubbles to serve as a gaseous pathway forlaser energy to pass from a laser fiber tip to the target. The resultinggaseous pathway has an absorption coefficient that is smaller than aliquid pathway. The bubble path effect is described in more detail inU.S. patent application Ser. Nos. 15/927,143, 16/177,800, 15/861,905,which are incorporated herein by reference. However, as will bedescribed in more detail below, bubble dynamics introduce manychallenges in establishing and maintaining a gaseous pathway between alaser fiber tip and a target to improve laser beam efficacy.

Accordingly, it is one aspect of the present disclosure to optimize theavailable laser energy to treat a target based on an enhanced bubblepath effect for targets which will be discussed in more detail below.The amount of energy needed to create a bubble path effect, that is, thecreation of an air tunnel between a tip of an optical (or laser) fiberand a target, is also a function of the distance between the tip of thefiber and target. Therefore, it is another aspect of the presentdisclosure, to reduce the amount of laser energy which may be wasted tocreate the bubble path effect for a specific distance to a tissuetarget, and thus to increase the amount of laser energy available totreat the target. It is yet another aspect of the present disclosure toincrease the distance of the bubble path effect and to reach targetsfurther away from the laser fiber tip for a specific laser energy.Utilizing the present disclosure can result in less wasted energy whentreating a tissue at a given distance or allow treating tissue furtherdistances away from the laser fiber tip for a given level of energy.

In some bubble path effect technologies, a first laser pulse may beprovided to create a first bubble through which a second laser pulse isprovided through the bubble after a predefined time delay. The secondlaser pulse is transferred with reduced absorption due to the firstbubble (and the relative absence of fluid) and reaches the tissue withhigher energy as compared to that of a single laser pulse travelingthrough a liquid medium only. Furthermore, the energies of the first andsecond pulse, as well as the time delay between the two pulses, may bevaried to achieve a higher energy delivery to the tissue, which ispresent at various distances from a tip of the laser fiber.

Infrared lasers, such as Holmium (Ho) lasers, having a wavelength of2100 nm and Thulium (Tm) lasers, having a wavelength in the range of1940 nm to 1970 nm, are strongly absorbed in a liquid environment. Forexample, the photons at 1940 nm wavelength have an absorptioncoefficient of 110 [1/cm] and the photons at 2100 nm wavelength have theabsorption coefficient of 25 [1/cm]. Typically, in a liquid environment,many of the photons produced by the Holmium laser are absorbed beforethe laser pulse travels a distance of 0.5 mm from where it exits theoptical fiber while the photons produced by the Thulium lasers areabsorbed before the laser pulse travels a distance of 0.1 mm from whereit exits the optical fiber. In comparison, a solid-state Holmium laseris characterized by high peak power and relatively short pulses, while aThulium fiber laser (TFL) is characterized by a lower peak power.Therefore, it takes a longer time for a TFL, compared to a solid-stateHolmium laser, to generate an equal amount of energy. For example, a TFLwill generate an energy of 0.5 Jules in a pulse duration of about 1milliseconds (ms) while it takes about 0.2 ms for a solid-state Holmiumlaser to generate the same amount of energy. As will be furtherdiscussed below, it has been observed that the life cycle of a singlebubble lasts about 0.2-0.3 ms. Moreover, it has been observed that thebubble, once initiated, has its own dynamic characteristics which is inmany aspects unrelated to the laser pulse (except for the pulse'sinitial characteristics at a very short time frame of a few tens ofmicroseconds). Based on the above, a short solid-state Holmium laserpulse may end before the bubble will reach its maximum size while alonger TFL pulse will last 3-4 bubble life cycles. The incorporatedreferences mentioned above describe how to optimize the timing and thedistribution of energies among the first and subsequent laser pulses tominimize the energy invested in bubble creation and maximize the amountof energy that reaches the target. Further, a Holmium laser with areduced peak power may be used to extend the usual short pulse duration.

However, spreading a Holmium laser pulse energy over a longer pulseduration, like that in the above-mentioned Thulium pulse, may result ina pulse duration which is longer than the life cycle of a single bubble.As in the case with Thulium, a laser pulse which is longer than the lifecycle of a single bubble results in the creation of a cascade ofmultiple bubbles. A cascade of multiple bubbles may create a gaseouspathway to the target. However, such a bubble cascade is characterizedby sequence of independent bubbles, which expand and collapse atdifferent times and at different locations along the pathway. As aresult, the effective length of the gaseous pathway changes over time.Gaseous discontinuations along the pathway, at different times andlocations, are filled with energy absorbing liquid and this will againincrease attenuation of the pulse produced by the laser. Thus, theenergy delivered to the target is frequently interrupted during thesebubble collapses in an unpredictable fashion, resulting in multiplesub-pulses during the pulse duration and a significant waste of energy.

Accordingly, one or more embodiments described herein provide foreffectively and efficiently manage the level of the laser energy alonglong laser pulses. In various embodiments, effective and efficientmanagement of laser energy during long laser pulses can provide one ormore of the following advantages: (i) laser energy delivered to thetarget at a given distance is increased, (ii) laser energy losses whilethe gaseous pathway to the target is being built are decreased, and(iii) stabilization of the pathway over the course of the pulse, asopposed to being subjected to stochastic collapses with unpredictableenergy deliver results. Many embodiments optimize the energydistribution along long laser pulses.

Several embodiments described herein provide to reduce, or prevent, heatbuildup in the surrounding tissues by more effectively delivering laserenergy to a target at lower energy levels to achieve the same level oftreatment. For example, laser energy may be delivered to a target at 30W instead of 40 W while achieving the same level of treatment. Manyembodiments may generate pulses that optimize the delivery of energythrough a water environment. In many such embodiments, when formed, theoptimized pulse may be used to obtain one of the following benefits: (1)using the same pulse energy to deliver more energy to the target at agiven distance resulting in faster/stronger intended effect on tissue,such as fragmentation, dusting, pop-corning, etcetera (improvedefficiency/efficacy); (2) using the same pulse energy to deliver energyto the target at a longer distance (better action at distance/action atlonger distances); and (3) using a lower pulse energy to obtain the sameintended effect as with a higher pulse energy, thus reducing unintendedside effects and adverse outcomes, such as over-heating of surroundingtissue (improved safety profile).

In some embodiments, a laser with low peak-power and long pulses, suchas a TFL, may be utilized so that the total size and stability of thebubble cascade generated is much longer (along the fiber axis from thelaser fiber tip to the target) than the single bubble of a typical shortpulse laser. Therefore, and unexpectedly, even though Tm photons havemuch stronger absorption in water than Ho, when comparing short pulse Hoto long pulse Tm, the latter travels further, as it travels through thelonger train of bubbles produced by the TFL. Further, a longer pulseduration takes better advantage of the cascade of bubbles as the pulsepersists while the bubbles reach the target. However, while it has beenobserved that the TFL pulses are severed into several sub-pulses due tothe multiple bubble collapses, resulting in a widely variable energydelivery during the pulse duration, the Ho laser energy may producesimilar energy delivery.

As mentioned above, the bubble has its own dynamics, and once initiated,in many aspects it is no longer related to the characteristics of thelaser pulse. An initial bubble formed by firing the laser first grows toa maximum size (dependent on the initial peak power of the pulse), andthen collapses. The typical bubble duration for a Holmium laser is−200-300[μs]. Laser pulses which are longer than the life cycle of thebubble, create several bubbles, in a series, emanating from the laserfiber tip towards the target.

FIG. 1 illustrates an exemplary diagram 100 of pulses of a Holmium laserand a Thulium laser according to one or more embodiments describedherein. In the illustrated embodiment, the Holmium and Thulium lasershave an equal energy of 0.2 Joules. Diagram 100 illustrates a typicalhigh peak-power Holmium laser short pulse versus low peak-powerquasi-continuous Thulium long pulse. The diagram 100 includes bubblesize on the positive y-axis 102 (with a potential target position atline 112), pulse power on the negative y-axis 104, and time on thex-axis 106. With respect to the high peak-power Holmium laser shortpulse, area 118 corresponds to the pulse power, curve 108 corresponds tothe bubble created, and line 114 corresponds to the effective distancethe laser pulse travels through liquid. With respect to the lowpeak-power quasi-continuous Thulium long pulse, area 120 corresponds tothe pulse power, curve 110 corresponds to the bubble created, and line116 corresponds to the effective distance the laser pulse travelsthrough liquid.

In both cases, after a short delay, on the order of a few tens ofmicroseconds (μs), following the laser pulse initiation, a bubble iscreated and starts to expand. In both cases, the life cycle of thebubble, once created, appears to have its own internal dynamics whichare not solely related to the laser pulse, and includes the internalvapor pressure generated in the bubble enucleation site, which in turncan depend on absorption, instantaneous peak power, laser beam quality,and/or the presence and amount of air pockets inside the liquid.

It takes time for the bubble to expand. In the case of the Holmiumpulse, the bubble reaches its maximum size well after the highest powerpeak of the laser and in the case of the Thulium laser, the bubblereaches its maximum size during the laser pulse. Also shown in FIG. 1 isthat for an exemplary target distance 112 (positioned at a distance ofabout 3 mm), the effective distance the Thulium laser pulse can travelthrough liquid 114 is much longer than the effective distance theHolmium laser pulse can travel through liquid 116. Several embodimentsdescribed herein take advantage of the independent dynamics of thebubbles in order to optimize the energy distribution using a long pulse.

FIGS. 2A and 2B illustrate exemplary diagrams 200A, 200B of Holmiumlaser short pulses in different mediums according to one or moreembodiments described herein. FIG. 2A corresponds to an air medium andincludes diagram 200A of pulse power over time 202 as measured in theair medium from a distance of 3 mm. FIG. 2B corresponds to a liquidmedium and includes diagram 200B of pulse power over time 206 asmeasured in the liquid medium from a distance of 3 mm. Additionally,FIG. 2B includes a time series of images of bubble dynamics 204corresponding to, and shown in synchrony with, the diagram 200B. In eachcase a sensor placed within an air or water pathway can be utilized tosense and record pulse power over time.

In the illustrated embodiment, the times series of images of bubbledynamics 204 were taken using a high-speed camera. As shown in the timesseries of images of bubble dynamics 204, a single index bubble wasinitiated after a short delay following the beginning of the laserpulse. Also shown in FIG. 2B is that the bigger the bubble, the higheramount of laser power reaches the target, which was a sensor in thisexemplary lab setting. The maximum energy is experienced by the targetwhile the bubble size (or bubble tunnel size) meets or exceeds thedistance to the target, resulting in only air between the fiber tip andthe target. Once the bubble starts to collapse, less laser power canreach the target. Also shown in FIG. 2B is that the bubble life cycle islonger than the laser pulse duration.

FIGS. 3A and 3B illustrates exemplary diagrams 300A, 300B of Thuliumlaser long pulses in different mediums according to one or moreembodiments described herein. FIG. 3A corresponds to an air medium andincludes diagram 300A of pulse power over time 302 as measured in theair medium from a distance of 2 mm. FIG. 3B corresponds to a liquidmedium and includes diagram 300B of pulse power over time 306 asmeasured in the liquid medium from a distance of 2 mm. Additionally,FIG. 3B includes a time series of images of bubble dynamics 304corresponding to, and shown in synchrony with, the diagram 300B. InFIGS. 3A and 3B, the pulse powers over time 302, 306 may correspond toan exemplary long pulse of Thulium laser of 0.2 Joule. In each case asensor placed within an air or water pathway is utilized to sense andrecord pulse power over time.

FIGS. 3A and 3B show the very different behavior of a long laser pulsein contrast to the short laser pulse of FIGS. 2A and 2B. Surprisingly,as shown in diagram 300B, the target in this case experiences twoseparate effective laser pulses 308 a and 308 b, although only a singlelong laser pulse was generated. The dynamics of the cascade of bubblescan provide the explanation. It is only after the gaseous pathway getsclose enough to the target that some energy reaches the target (in thecase of Tm, most energy is absorbed in water within 0.1 mm). Further, ittakes time for the gaseous pathway to come close enough to the target,and during this time, no laser power reaches the target. Instead, thelaser power is mainly absorbed by the liquid in the way to the target.As previously mentioned, energy absorbed by the liquid is not availableto treat the target and may turn into unwanted heating of surroundingtissues.

Due to the lower peak power, in comparison to FIGS. 2A and 2B, it takesmore time for the gaseous pathway to expand close enough to the targetand for energy to reach the target. Moreover, in the case of the Thuliumlaser, which is more absorbed by water than Holmium, the rising profileof the laser (as well as the falling time) as experienced by the targetis much steeper than it is in the Holmium case, as can be appreciated bya comparison of the diagrams 200B and 300B. Many embodiments describedherein may utilize a predetermined pulse energy and a distance to thetarget to control and optimize the power modulation along the pulse sothat more laser power is available during an effective pulse experiencedby a target, and less laser power is lost between effective pulses. Inmany such embodiments, a user may select the pulse energy.

Referring now to the time series of images of bubble dynamics 304 ofFIG. 3B, several of the images (or frames) of the time series arenumbered, 1-23 from left to right. More specifically, frame #1 shows thetip of the fiber before the initiation of the laser pulse. Once thelaser pulse starts, an index bubble, shown in frame 2, starts to growrelatively spherically at the tip of the fiber. As this index bubblecontinues to grow, it can be seen in frame 3 and 4 that at its frontedge, a second bubble starts to grow in a forward direction. Moreover,since this second bubble is an extension of the index bubble, the highpressure inside the index bubble shapes the second bubble to a morecylindrical shape. In addition, as pressure is drained from the indexbubble into the second bubble, the index bubble expansion decreases. Theresult of these two processes is that most of the inside pressure inthese two bubbles expands mainly forwardly toward the target as can beseen in frames 5-7.

At this stage, according to the example, the gaseous pathway has reachedclose enough to the target so that the target experiences the laserpower. It is another aspect of the disclosure to generate an indexbubble, to generate a second bubble at the front edge of the indexbubble and to let the index bubble to inflate and shape the secondbubble spontaneously while modulating down the laser pulse power duringthat time to a lower level than the level which is required to initiatethe index bubble. Furthermore, the index bubble at the tip of the fibertends to collapse on tip of the fiber itself and may degrade it. As aresult, the laser beam quality may be reduced as well as the treatmentefficiency. The higher the laser power during the initiation of theindex bubble, the higher the internal pressure inside the index bubbleand the stronger the cavitation effect on the tip of the fiber once theindex bubble collapses. Therefore, in an embodiment of the presentdisclosure a minimum laser power needed to initiate an index bubble isused, followed by a decreased laser power during the expansion of theindex bubble while the laser power is increased again only after theindex bubble starts to collapse to further build additional bubbles anda gaseous pathway to the target. Reducing the cavitation effect on thetip of the fiber may delay its degradation.

Referring now to frame 9, it can be seen that the index bubble starts tocollapse, and the second bubble breaks off and away from the collapsedindex bubble. As seen in next frame 10, fluid fills up the gap betweenthe separated bubbles, and also collapsing second bubble, and thecollapsing index bubble. As a result, the target starts to experience adecreased power of laser until no energy reaches the target around frame11. Also, in frame 10 and more clearly in frame 11, it can be seen thatanother index bubble is initiated and starts to expand at the tip of thefiber. At this stage, a similar process which was described aboveregarding fames 1-5 takes place where the gaseous pathway has to berebuilt, and it is only until the pathway reaches close enough to thetarget before it starts to experience again an exposure to laser powerin around frame 16.

Accordingly, many embodiments described herein may modulate down thelaser power once an index bubble has been initiated and during thebuildup of the gaseous pathway to the target. Many such embodimentsthereby optimize the energy distribution along long pulses to make thebubble path effect more efficient in light of the independent lifecycles of the bubbles.

FIGS. 4A-4B and FIG. 5 illustrate various aspects of Thulium long laserpulses according to one or more embodiments described herein. Morespecifically, FIG. 4A illustrates an exemplary diagram 400A of a Thuliumlaser long pulse in an air medium with pulse power over time 402; FIG.4B illustrates an exemplary diagram 400B of a Thulium laser long pulsein a liquid medium with pulse power over time 404; and FIG. 5illustrates an exemplary time series of images of bubble dynamics 500corresponding to diagram 400B.

Referring to FIG. 4A, the pulse power over time 402 of a long Thuliumlaser pulse, in an air medium, of about 1 ms in duration and whichgenerates 0.5 Joule as measured from a distance of 2.5 mm is shown indiagram 400A. The corresponding measurement in a liquid medium is shownin FIG. 4B. The pulse of FIGS. 4A and 4B are longer than the pulse shownin FIGS. 3A and 3B. As such, the target experiences 4 effective laser“sub-pulses” 406 a, 406 b, 406 c, 406 d, as shown in FIG. 4B, as opposedto the two effective laser “sub-pulses” 308 a, 308 b discussed inrelation to FIG. 3B. As previously mentioned, and shown in FIG. 4A, thelaser is quasi-continuously on for about 1 ms. However, effectively, atarget in this example, experiences four separated laser sub-pulses 406a, 406 b, 406 c, 406 d. These four separated effective laser pulses 406a, 406 b, 406 c, 406 d are the result of the creation and destruction ofthe gaseous pathways during the time that the laser is on. Severalembodiments described herein may modulate the power of the laser downduring the time that the gaseous pathways are built, thereby allowingthe spontaneous expansion of the bubbles, and saving laser energy untilthe gaseous pathway is close enough to the targe tissue. Further, when agaseous pathway is close enough to a target, embodiments may modulatethe laser power up and the utilize the gaseous pathway to bring higheramounts of laser power to the target.

Providing further laser energy during bubble expansion may waste energybecause the bubble will not grow further in size during the initialpulse energy applied, since that would mean “pushing against air” withinthe bubble. In other words, there may be no further absorption withinthe bubble after it starts expanding. To increase the size of the bubbleuntil the target is reached, laser energy may be expended only whilethere is liquid in the path from the laser fiber tip to the target sothat the resulting absorption is translated into pressure which inre-expands the bubble. Then, when the gaseous pathway starts to breakdown and develop liquid bridges between separated gaseous pockets, tomodulate the laser power down again until the next opportunity todeliver higher laser power to the target through another effectivegaseous pathway. FIG. 5 shows the images of the bubbles cascade dynamicsdiscussed above in relation to the FIG. 4B.

A Thulium Fiber Laser (TFL) is typically pumped by a diode laser tocreate long pulses. Further, a TFL produces a long pulse regime.Accordingly, one or more embodiments described herein may leverage thefact that the time constants associated with bubble formation,initiation, expansion, and collapse are shorter than the laser pulselengths to modify the pulse power during long laser pulses. In contrast,short pulse lasers are usually pumped by flash lamps, which themselvesoperate in very short pulse regimes. Short pulse lasers operate in adomain in which the bubble life cycle is longer than the laser pulselength. However, embodiments described herein provide a variety oflasers arranged to emit light having a high absorption coefficient inthe relevant liquid and which may generate pulses that are longer thanthe life cycle of the bubble, and further which may be modulated up anddown. For example, one or more of Yttrium Aluminum Garnet (YAG), Erbium,Holmium, and other IR diode or solid state lasers may be modulated upand down according to the present disclosure without departing from thescope.

Various embodiments described herein may utilize a distance between thetip of the optical fiber and the target to determine a mode ofoperation. For example, there could be two (or more) different scenariosor settings, which might be selected (often automatically by the lasersystem) based on the distance from the tip of the optical fiber and thetarget. In a first example scenario, the index bubble expands to a largeenough distance and gets close enough to the target for delivery oflaser energy. In a second example scenario, the expansion of the indexbubble alone is not enough to get close enough to the target and atleast a second bubble is required to further expand the gaseous pathwaybefore the target may be treated. In the first scenario, and inaccordance with the present disclosure (e.g., see various V-shapetechniques described below), once the index bubble is created, the powerof the laser is modulated down until the index bubble gets close enoughto the target. Once the index bubble gets close enough to the target,the power of the laser is modulated up to treat the target. In thesecond scenario, and in accordance with the present disclosure (e.g.,see various resonant modulation techniques described below), once theindex bubble is generated the laser power is modulated down and it ismodulated up again to treat the target once the second or third bubblereaches the target and when the gaseous pathway starts to break thelaser power is modulated back down.

As discussed above, different wavelength and types of laser emissionshave different absorption coefficients in a liquid working environment.Therefore, to be “close enough” to a target is a function of the laserand may represent different distances for different lasers. As discussedabove in relation to FIGS. 3B and 4B, the slope of the rising profile ofan effective laser pulse a target experiences, is also a reflection ofthis distance. For example, a Thulium laser is absorbed more strongly inthe liquid than a Holmium laser. Accordingly, only when the gaseouspathway reaches a distance to the target in a magnitude close to that aThulium laser photons can travel in the liquid, the target may start toexperience some laser power impact. However, since Holmium laser photonsmay travel in the liquid environment a longer distance than Thulium, theslope of the rising effective laser pulse is less steep. It follows thata close enough distance to a target for a Thulium laser is a shorterdistance than it is for a Holmium laser. Since this disclosure may berealized and practiced by different lasers, it will be appreciated thatthe notion of being close enough is a function of the laser used and thedistance its photons can travel in the liquid environment.

Bubble dynamics generally have two phases, expansion followed bycollapse. Further, this dynamic has its own time constants. During thisbubble expansion, in which the bubble expands, further delivery of laserpulse power (power=rate of energy) appears not to effectively act on thebubble itself, as there is nothing inside the bubble to push against(i.e. there is no or very few absorption media inside the bubble).

Thinking of the harmonics of the operation of a playground-type swing asan analogy, in order to effectively increase the swing's amplitude, the“pushing” frequency should be matched to the swing's natural frequency.In other words, a pulse will be most effective at increasing bubble sizeif it is “resonant” with the bubble natural frequency (f˜1/200[us] ˜5000[Hz]). Accordingly, various embodiments described herein may modulatelaser pulses based on the natural frequency of a bubble.

In various embodiments, laser pulses may be modulated based on thenatural frequency of a bubble as follows. A quasi-continuous wave (QCW)laser that is suitable to also being powered up and down during a longquasi-continuous pulse may be used, such as a TFL. In many embodiments,powering up and down during quasi-continuous pulses may be accomplishedby generating fluctuating power. Further the fluctuating power may begenerated by driving the pumping laser sources at variable currentswhile integrating over time to deliver a requested pulse energy (PE). Invarious embodiments, the overall integral of the modulated power overtime equals the requested PE as defined by the user. According to someembodiments, power may be at its highest at the start of the pulse, forexample, at the maximum power deliverable by the system.

Once an index bubble is initiated, the power may preferably then bereduced until the bubble is at its max size, thus providing a “reserve”of laser energy that may be better utilized to impact the target oncethe gaseous pathway gets close enough to the target. At the time thebubble starts to collapse, power may preferably be fluctuated back toits maximum level. This should be repeated in cycles, with a periodapproximately or substantially equal to the bubble lifetime.

Since in some cases the target may move (in the case of a kidney stonefor example) or, even if the target is more or less stationary withrespect to the laser fiber tip, the distance between the laser fiber tipand the target may differ depending on the anatomy of the person or thepractical access to the target by the laser fiber tip, or destruction ofthe target during a procedure. Accordingly, the power fluctuationtechnique may be varied based on the distance between the laser fibertip and the target. For example, when the distance to a target ischanged (e.g., due to a movement of the target and/or the optical fiber,due to patient anatomy or target changes, or the like) such a distancechange may be measured, monitored, or estimated so that the power of thelaser may be adjusted accordingly on the fly. Accordingly, when thedistance increases/decreases, the system may recalculate the length ofthe pulse required to create enough effective pulses and/or to exposethe target to enough laser energy in order to meet the clinical effectrequired. For example, with distant targets, the number of cycles may beincreased in order to provide a clear, stable, liquid free path from thelaser fiber tip to the target.

FIG. 6 illustrates an exemplary diagram 600 of laser pulse powermodulation 604 in relation to bubble size 602 according to one or moreembodiments described herein. In various embodiments, diagram 600includes an exemplary pulse power modulation scheme. A pulse modulationscheme may include one or more settings, modes, parameters,characteristics, features, and the like of the pulse, the environment(e.g., liquid medium, distance), and/or various components utilized toimplement the pulse (see e.g., laser system 900). The pulse powermodulation 604 is shown by a sinusoidal-type pattern shown in theslanted hatched area. In this case, power is modulated from a high levelof 500 W to a low level of 300 W. According to this aspect of thedisclosure, the laser power over long pulses is modulated in an oppositedirection to the bubble dynamics described above so that when the bubbleexpands the laser is modulated down and when the bubble collapses thelaser is modulated up. Embodiments are not limited in this context.

FIG. 7 illustrates an exemplary diagram 700 of modulated and unmodulatedlaser pulses in conjunction with associated bubble dynamics according toone or more embodiments described herein. Diagram 700 shows an exemplarycomparison between an unmodulated long laser pulse scheme 704 a and itsassociated bubble dynamics 704 b and a modulated long pulse scheme 702 aaccording to the present disclosure and its associated bubble dynamics702 b. The diagram 700 includes pulse power on a first y-axis 706,bubble size on a second y-axis 708, and time on the x-axis 710. Invarious embodiments, FIG. 7 may correspond to bubble path resonantmodulation techniques. For instance, the laser pulse may be fit tobubble dynamics to cause bubble size resonation, leading to increasedenergy delivery to a target.

The flat, unmodulated, long pulse 704 a shown in FIG. 7 may cause acascade of bubbles which expand and collapse in a sinusoidal pattern(corresponding to bubble dynamics 704 b). Moreover, the bubbles from theunmodulated pulse 704 a grow to about the same size and collapse toabout zero size repeatedly in an uncontrolled way. In other words, sincethere is no mechanism to control or synch the timing and/or location ofthe bubble collapse and the laser power pulses there is only randomconstructive and destructive interactions. As will be appreciated, theamount of energy invested in the process is equal to the area below thepulse power line 704 a (the integral of the power over time). However,when the laser power is modulated in an opposite direction to the bubbledynamics (see 702 a, 702 b), energy is saved during the expansion of thebubble. Further, the higher energy modulation during bubble collapsing,reduces the pace of collapse, and accelerates the formation of the nextbubble. The accelerated creation of the second bubble takes place beforethe previous bubble collapses to a zero size and vanishes. Therefore,the second bubble starts from the “shoulders” of the first bubble andreaches further distance. Accordingly, many embodiments described hereinmay utilize a pulse modulation scheme (e.g., 702 a) whereby the samedistance reached by the unmodulated pulse 704 a is reached while usingless laser energy.

FIG. 8 illustrates an exemplary diagram 800 according to one or moreembodiments described herein. Diagram 800 shows an exemplary pulsemodulation scheme 810 in conjunction with its associated bubble dynamics812. The diagram 800 includes pulse power on a first y-axis 802, bubblesize on a second y-axis 804 (with a target position line 808 at 2 mm),and time on the x-axis 806. In various embodiments, FIG. 8 maycorrespond to bubble path resonant modulation techniques. For instance,a target distance may be utilized to create a correspondingly sizedbubble prior to delivering a pulse burst.

The pulse modulation 810 illustrated in diagram 800 works in a counterdirection to the bubble size dynamics 812. In this example, the targetis located at a distance of 2 mm from the tip of an optical fiber (seeline 808). As shown in the illustrated embodiment, since the power ofthe laser is modulated up when the bubble size starts to shrink, thebubbles do not collapse to a zero size, or the collapse is at leastreduced. Every successive bubble is built on the “shoulders” of itsprevious bubble, creating a step wise pattern until the gaseous pathwayreaches close to the target. As used herein, close to the target can betaken to mean less than or equal to a threshold distance. In manyembodiments, the threshold distance may be determined based on one ormore of the wavelength of the laser beam, its associated waterabsorption coefficient, and the maximum available power of the laserbeam. For example, the threshold distance may be approximately 0.1 mmwhen using a Thulium laser and approximately 0.5 when using a Holmiumlaser.

Once the gaseous pathway is built, the laser power is switched (orramped up) to its maximum power (or the power setting associated withthe desired treatment) so that most of the pulse energy may be deliveredto the target. In various embodiments, the laser energy transfer in aliquid medium may be a function of the laser pulse shape in the air, thedynamic of the bubble front over time, and the delay between theinitiation of the laser pulse and the initiation of the bubble.

While the above discussion has generally been directed to treatingtargets at a distance, an alternative pulse modulation profile toimprove energy delivery at relatively nearby target distances may be thetermed as a “V-shape”. In various embodiments, nearby targets may bedefined as those located at distances that can be bridged by the indexbubble alone, and distant targets may be defined as those located atdistances which are 2 to 4 times the size of the index bubble, requiringa “train of bubbles” to deliver sufficient energy to the target.Different lasers may result in different index bubble sizes. Forexample, an index bubble for a Holmium laser may be approximatelybetween 1 mm and 2 mm and an index bubble for a Thulium laser may beapproximately between 0.5 mm and 1 mm.

In various embodiments, a V-shape pulse modulation may have one or moreof the following profile characteristics: (a) start with maximal powerto create initial bubble; (b) drop power while bubble expands; and (c)increase power back to maximum while bubble is at its maximal size orwhen the bubble is expected to reach the target (whichever is shortest).In various embodiments, this V-shape pulse modulation would result inmore efficient energy delivery than a Holmium laser short mode (whichresembles a downward slope triangle) because it delivers more of thepulse energy during the expanded phase of the bubble, thus encounteringless water absorption.

In various embodiments, the laser power and a distance between the fibertip and the target may be provided as input for optimizing the pulsemodulation. The index bubble maximal size may be a function of theinstantaneous pulse power during the first few 10 s of microseconds aswell as of the wavelength absorption in water, beam quality, anddelivery fiber geometry. Accordingly, for a given laser and deliveryfiber, the bubble dynamics for various peak powers can be measured, suchas in a bench setup. A lookup table may be created to tabulate therelationship between {peak power and/or initial power, fiber size, andwavelength} vs. {max bubble size, time from lasing initiation to startof bubble formation (t0), time to reach bubble maximum size (tmax), andtime to collapse (tc)}. From this information, the initial modulationfrequency may be obtained as roughly 1/(tc−tmax−t0). Further insightinto modulation frequency dynamic adjustment may be derived byexperimental observation in the bench setup of modulation frequencychange effects on vapor tunnel stability and energy delivery distancewithout departing from the scope of this disclosure. The index bubblesize as a function of time may be strongly dependent on pulse (peak)power and the absorption coefficient of the liquid at the laserwavelength. Accordingly the pulse (peak) power and the absorptioncoefficient of the liquid at the laser wavelength may be utilized toestimate the time an index bubble reaches its maximal size and starts tocollapse.

FIG. 9 illustrates an exemplary laser system 900 according to one ormore embodiments described herein. In various embodiments, laser system900, or one or more components thereof, may be utilized to implement oneor more of the techniques described herein, such as one or more of thepulse modulation schemes. In many embodiments, laser system 900 may be,or include, a fiber laser. In the illustrated embodiment, laser system900 includes a laser source 921 capable of producing a laser beam 923, acontroller 922, laser fiber 924 (or optical fiber 924), connector 925, apartially transparent mirror 926A, a partially transferred mirror 926B,a photodetector 927, and a distance measurement module 929 that utilizesreflected light 928 to dynamically measure the distance between the tipof the laser fiber 924 a target (not shown). In various embodiments, aknown apparatus (e.g., an endoscope) may be utilized to introduce thelaser fiber 924 into a body cavity for positioning the tip of the laserfiber 924 proximate to a target, such as a kidney or other urinary tractstone or a prostate that is to be treated by ablation or enucleation.One or more components of FIG. 9, or aspects thereof, may beincorporated into other embodiments of the present disclosure, orexcluded from the described embodiments, without departing from thescope of this disclosure. For example, distance measurement module 929and/or photo detector 927 may be excluded from laser system 900 withoutdeparting from the scope of this disclosure. Embodiments are not limitedin this context.

The laser source 921 of system 900 may produce the laser beam 923 whichis transmitted through the connector 925 to the laser fiber 924 andthence to the target. The system also includes a controller 922. FIG. 9illustrates schematically one embodiment of the present invention. Lasersystem 900 consists of a laser module 921 and a control unit 922. Alaser beam 923 exiting laser source 921 is configured to reach anoptical fiber 924 through connector 925. Partially transparent mirror926A located along the optical path of beam 923 and is configured toreflect, at least a portion of beam 923 into photodetector module 927.Some of the backscattered light from a target enters optical fiber 924,passes through connector 925, and is configured to target partiallytransferred mirror 926B and enter into distance measurement module 929.Module 929 is configured to measure the distance between the tip ofoptical fiber 924 and a target. Modules 927 and 929 are also controlledby programmable controller 922. In some embodiments, during operation,programmable controller unit 922 may receive a first electrical signalfrom module 927 indicative of the energy level of the laser pulse and/ora second electrical signal from distance measurement module 929indicative to a distance change between the tip of optical fiber 924 anda target. In various embodiments, laser system 900, based on at leastone of the first and second indicative signals, may be configured toadjust one or more operating parameters, such as the amount of thecurrent supplied to the laser pumping element to keep energy levelswithin target parameters and in accordance with any dynamic change inthe laser performance or the distance to a target. Some aspects of thesystem 900 are described in more detail in U.S. Pat. No. 10,231,781,(the '781 patent), the entire disclosure of which is herein incorporatedby reference.

It will be appreciated that one or more embodiments described hereby maybe implemented without one or more of photo detector 927 and distancemeasurement module 929. In some embodiments, a distance between a fibertip and a target may be an expected or predetermined distance. Forexample, the predetermined distance may be based on a mode of the lasersystem. In another example, the predetermined distance may be based onuser input. Further, in some embodiments, modulation schemes may beselected based on a mode of operation and/or user input.

In various embodiments, the controller 922 may include a processor andmemory comprising instructions that when executed by the processor causethe processor to perform one or more techniques or aspects describedherein. In many embodiments, the controller 922 may initiate andregulate the power emanating from the laser source 21. In someembodiments, the controller 922 may measuring the distance from the tipof the laser fiber to the target. In other embodiments, the distance maybe provided as input to the controller 922. For example, distancemeasurement module 929 may provide the distance as input to controller922. Techniques for determining distance between the tip of the laserfiber and the target are described in more detail in U.S. Pat. No.9,017,316 and U.S. Provisional Patent Application No. 63/118,857, theentire disclosures of which are herein incorporated by reference.Depending on the distance measured, the controller 922 may initiate andregulate the amount of power which is provided to the laser fiber, andin the context of the present disclosure, the varying powerconfigurations (modulation schemes) described herein.

In many embodiments, the laser system 900 may operate in different modesfor nearby targets and distant targets. As previously mentioned, forexample, V-shape optimization may be utilized to determine pulsemodulation schemes for nearby targets and resonant modulationoptimization may be utilized to determine pulse modulation schemes fordistant targets. In various embodiments, the controller 922 maydetermine which optimization and/or modulation scheme to use based, atleast in part, on the distance to the target.

For V-shape optimization on nearby targets, the inputs may include pulseenergy and a target at close proximity (“contact”/“close”). As describedabove, the term “close proximity” can mean that the target is within adistance from the tip of the laser fiber 924 that can be bridged by theindex bubble alone. In such a scenario, the initial pulse power may bedetermined to deliver a bubble of size approximately (or substantially)1 to 2 times the distance to the target. Max energy delivery may occurwhile the bubble is equal to and larger than the distance to the target.Accordingly, in some embodiments, bubble size may be utilized to controlan amount of time maximal energy is delivered to a target. For example,a bubble size approximately two times the distance to the target may beutilized to deliver maximal energy for a relatively long period of timeand a bubble size approximately equal to the distance to the target maybe utilized to deliver maximal energy for a relatively short period oftime. In some embodiments, the controller 922 may determine the initialpulse power. The laser may be fired at the initial pulse power and thenmodulated down until the time the bubble is near maximal size. Then thepulse power may be raised to maximum. In some embodiments, when theinitial pulse power is equal to the max power the system may start atmax power, reduce power during bubble expansion, and raise to max poweragain when the bubble is at maximal size. Finally, the pulse may beterminated when the integral (power×time) is equal to the requestedpulse energy. As used herein, “max power” may not mean the maximum powerwith which the laser source can deliver, but instead can mean the powerlevel for the desired therapy or treatment.

For resonant modulation optimization on distant targets, the inputs mayinclude pulse energy and a target at distance (“distance” mode). Theinitial pulse power may be set at the maximal system power. For example,controller 922 may set the initial pulse power to the max level based onclassification of a target as distant based on a distance estimation.The laser may be fired at the maximal power level and then modulateddown during bubble expansion. The power may be modulated up to max againwhen the bubble reaches maximal size. Then the modulation may be cycledat periods in the range of 0.5 to 1.5 times the bubbleexpansion/collapse dynamics (e.g., ×0.7-×1.3 of the time from start tocollapse) to achieve a resonant effect. In various embodiments, theperiod may be adjusted for each sequential bubble in the bubble train,such as due to changes in the distance to the target. When the train ofbubbles is expected to bridge the distance to the target, the pulsepower may be raised to max to take advantage of minimal liquid beinglocated along the pathway of the laser between the fiber tip and thetarget. Finally, the pulse may be terminated when the integral(power×time) is equal to the requested pulse energy.

In one embodiment, a method of operating the laser system 900 mayinclude one or more of the following exemplary operational steps of thelaser system 900, which is configured to implement one or more pulsemodulation schemes described herein. Step one, a user selects the typeof fiber in use. According to one embodiment, a user may select manuallya type of fiber to be used in the treatment. According to anotherembodiment, an automatic fiber recognition system may be implemented.Step two, a user may select the required treatment energy level. Thepulse energy defined by the user for the treatment may be the overallenergy expected to be emitted by the laser system in a modulated pulse.In other words, and as will be discussed below, the system may beprogrammed and configured, using a suitable programmable controller, toset up a pulse modulation scheme in a way transparent to the user. Forexample, the user in this embodiment may not be required to set up thevalues for various parameters.

Step three, a user may select the modulation scheme repetition rate(e.g., the time between modulated pulses). Step four, a user may selecta desired (average) working distance between the tip of the fiber andthe target tissue. According to another embodiment, the working distancemay be detected by the system automatically, for example, by using adistance evaluation technology as described in the U.S. patentapplication Ser. No. 13/811,926, the entirety of which is incorporatedherein by reference. Step five, based on previously manually loaded orautomatically detected parameters, the system may define automatically,from a lookup table operatively associated with the programmablecontroller or calculates the working values for one or more of peakpower, initial power, fiber size, wavelength, max bubble size, time fromlasing initiation to start of bubble formation (t0), time to reachbubble maximum size (tmax), and time to collapse (tc).

Step six, a pulse may be fired according to the modulation scheme. Invarious embodiments, the system may be configured to measure actualvalues of each pulse/modulation scheme. In step seven and eight, thesystem may be configured to compare the measured values to thepredefined values on step five. Should the measured parameters deviatefrom the predefined parameter, the system automatically corrects suchdeviation in step nine, and a new set of working parameters are sent tothe programmable controller which for implementation in the nextmodulation scheme by repeating at step six. In this way, the system maymaintain the actual working values within the predefined range. Itshould be understood that during step seven, the system may beconfigured to measure different parameters which may be related toactual laser pulse energy.

For example, according to one embodiment, the system may usephotodetector 927 to measure optical energy output of the modulationscheme. According to another embodiment, for example, the system may beconfigured to measure current or voltage pulses which are sent to thelaser pumping energy source. Therefore, the feedback loop may beconfigured to feedback, based on each measured parameter, whether thisis a measured optical value, a measured current value, a measuredvoltage value, or any other measured parameter which is related to apulse modulation scheme.

In some embodiments, a method of operating the laser system 900 may beloosely based on FIGS. 3A and 3B of the '781 patent, accounting, ofcourse, for any differences in the laser source, and the sequence oflaser firings described herein, as illustrated in the flowchart of FIG.10.

FIG. 10 illustrates an exemplary process flow 1000 (or method 1000)according to one or more embodiments described herein. In process flow1000, a subset of operation steps may include measuring the distancefrom the laser fiber tip to the target at block 1002. For example,controller unit 922 can determine a distance between the tip of thelaser fiber 924 and a target. More specifically, circuitry of controllerunit 922 and/or distance measurement module 929 can execute instructionsand/or receive signals to determine a distance between the tip of thelaser fiber 924 and the target. At decision block 1004, if the distancemeasured is less than or less than or equal to a distance (D) X, thenthe method 1000 can proceed to a V-shape mode; if, however, the distanceD is greater than or greater than or equal to the distance X, the methodcan proceed to a modulation mode of operation. In various embodiments,the distance X may be determined experimentally and the results recordedin a lookup table which includes distances as well as other parameterssuch as the number of pulses and the power applied to the pulses. Itshould also be mentioned that since the target may be mobile in itsenvironment, such as a kidney stone, the controller may be dynamic innature and able to adjust parameters for the laser, including changingfrom a V-shape mode to a resonant modulation mode, and vice versa, basedon repeatedly determining the distance D and repeatedly determiningwhether the distance D is greater than or less than X. Embodiments arenot limited in this context.

After the mode is selected (e.g., at block 1006 or block 1020), method1000 include selecting parameters for the selected mode. For example,the controller 924 can select the number of pulses and the energy levelto be applied to the target (block 1008, 1022). More specifically, wherethe V mode is selected at block 1006, controller 924 can select anenergy level of the pulses; and where the resonant mode is selected atblock 1020, the controller 924 can select an energy level of the pulsesand a modulation frequency for the pulses.

Continuing to block 1010 and 1024, method 1000 can include sendingcontrol signals to the laser source 921 to cause the laser source toactivate to fire the laser beam (block 1010, 1024), whereupon the method1000 includes operations for the controller 924 to calculate the pulseenergy delivered to the target (block 1012, 1026). For example,controller 924 can determine (or receive signals from sensors comprisingindications of) pulse energy delivered to the target. In addition, atblocks 1012 or 1026) the controller 924 may estimate one or more of thenumber of effective pulses to be experienced by a target, the effectiveenergy per every single effective pulse to be delivered to the target,and the accumulated effective energy to be delivered to the target bythe number of effective pulses. Moreover, for a selected energy level asmay be selected by a user, the controller 924 can select the powermodulation and bubble path modulation resonant frequency so that theselected energy is actually delivered to the target in one of moreeffective pulses.

If the controller selections were sufficient (block 1014, 1028) toachieve the desired effect (stone breakup, dusting, etc.), the operatorobserving the extent of treatment may stop the system (block 1016, 1032)and vice versa if the effects are not achieved (block 1018, 1030).Accordingly, method 1000 can include receiving an indication from anoperator (e.g., physician, or the like) that the treatment is sufficientor not. Based on the received indication, method 1000 can either end(block 1016, 1032) or can repeat (block 1018, 1030) or said differently,return to block 1002. In this manner, the operator may provide anindication to the system (e.g., system 900) and the system 900 canreceive the indication and further or additional treatments carrier outto reach the desired effects. The steps may be adjusted dynamicallyusing a closed feedback circuit connected to the controller. Thus, byway of example, if the distance to the target changes during theprocedure, the closed feedback loop may provide that information to thecontroller which then may cause the controller to change the parametersof treatment.

FIG. 11 illustrates a flowchart showing a method 1100 of implementing amodulation scheme in accordance with some embodiments of the presentdisclosure. The method 1100 is described with reference to the system900 and to the various configurations and embodiments described above.It is to be appreciated however, that the method 1100 could beimplemented using a system different than that described herein.Embodiments are not limited in this context.

At block 1102, the method 1100 includes determining a pulse energy for afiber laser. For example, controller 922 may determine a pulse energyfor laser source 921. In some embodiments, controller 922 may determinethe pulse energy based on input received via a user interface. In otherembodiments, controller 922 may determine the pulse energy based on oneor more settings of the laser system 900. At block 1104, the method 1100includes identifying a distance between a tip of the fiber laser and atarget, wherein a liquid is located between the tip of the fiber laserand the target. For example, controller 922 may identify determine adistance between the tip of laser fiber 924 and a treatment target basedinput from distance measurement module 924. At block 1106, the method1100 includes determining a modulation scheme based on the distance. Forexample, controller 922 may select between V-shape modulation schemesand resonant modulation schemes based on the distance between the tip oflaser fiber 924 and a target.

At block 1108, the method 1100 includes setting an initial pulse powerfor the modulation scheme to generate an index bubble in the liquidbased on the distance. For example, when the distance is over athreshold distance, the initial pulse power may be set to a maximalsystem power. In another example, when the distance is under a thresholddistance, the initial pulse power may be set to deliver a bubble with asize that is 1 to 2 times the distance to the target. In some suchexamples, a lookup table may be used to determine the initial pulsepower that will deliver the bubble with a size that is 1 to 2 times thedistance to the target. At block 1110, the method 1100 includesinitiating a pulse according to the modulation scheme via the fiberlaser, wherein the modulation scheme reduces power of the pulse afterinitiation of the pulse at the initial pulse power. For example,controller 922 may initiate a pulse according to modulation scheme 702a, or modulation scheme 810, via laser source 921 and laser fiber 924.

FIG. 12 is a block diagram of an exemplary computer system forimplementing embodiments consistent with the present disclosure. In someembodiments, FIG. 12 illustrates a block diagram of an exemplarycomputer system 1200 for implementing embodiments consistent with thepresent disclosure. In some embodiments, the computer system 1200, orone or more portions thereof, may comprise controller 922. In some suchembodiments, the computer system 1200 may be utilized to controloperation of laser system 900 with respect to a target. Embodiments arenot limited in this context.

The computer system 1200 may include a central processing unit (“CPU” or“processor”) 1202. The processor 1202 may include at least one dataprocessor for executing program components for executing user orsystem-generated business processes. A user may include a person, aperson using a device such as those included in this disclosure, or sucha device itself. The processor 1202 may include specialized processingunits such as integrated system (bus) controllers, memory managementcontrol units, floating point units, graphics processing units, digitalsignal processing units, etc. The processor 1202 may be disposed incommunication with input devices 1211 and output devices 1212 via I/Ointerface 1201. The I/O interface 1201 may employ communicationprotocols/methods such as, without limitation, audio, analog, digital,stereo, IEEE-1394, serial bus, Universal Serial Bus (USB), infrared,PS/2, BNC, coaxial, component, composite, Digital Visual Interface(DVI), high-definition multimedia interface (HDMI), Radio Frequency (RF)antennas, S-Video, Video Graphics Array (VGA), IEEE 802.n/b/g/n/x,Bluetooth, cellular (e.g., Code-Division Multiple Access (CDMA),High-Speed Packet Access (HSPA+), Global System For MobileCommunications (GSM), Long-Term Evolution (LTE), WiMax, or the like),etc.

Using the I/O interface 1201, computer system 1200 may communicate withinput devices 1211 and output devices 1212. In some embodiments, theprocessor 1202 may be disposed in communication with a communicationnetwork 1209 via a network interface 1203. In various embodiments, thecommunication network 1209 may be utilized to communicate with a remotedevice 1220, such as for accesses look-up tables or utilizing externalresources. The network interface 1203 may communicate with thecommunication network 1209. The network interface 1203 may employconnection protocols including, without limitation, direct connect,Ethernet (e.g., twisted pair 10/100/1000 Base T), Transmission ControlProtocol/Internet Protocol (TCP/IP), token ring, IEEE 802.11a/b/g/n/x,etc. In some embodiments, one or more portions of the computer system1200 may be integrated into the laser system 900. In some suchembodiments, one or more components of the laser system 900 may comprisean input device 1211 and/or an output device 1212 (e.g., distancemeasurement module 929, laser source 921, photodetector 927, etcetera).

The communication network 1209 can be implemented as one of thedifferent types of networks, such as intranet or Local Area Network(LAN), Closed Area Network (CAN) and such. The communication network1209 may either be a dedicated network or a shared network, whichrepresents an association of the different types of networks that use avariety of protocols, for example, Hypertext Transfer Protocol (HTTP),CAN Protocol, Transmission Control Protocol/Internet Protocol (TCP/IP),Wireless Application Protocol (WAP), etc., to communicate with eachother. Further, the communication network 1209 may include a variety ofnetwork devices, including routers, bridges, servers, computing devices,storage devices, etc. In some embodiments, the processor 1202 may bedisposed in communication with a memory 1205 (e.g., RAM, ROM, etc. notshown in FIG. 12) via a storage interface 1204. The storage interface1204 may connect to memory 1205 including, without limitation, memorydrives, removable disc drives, etc., employing connection protocols suchas Serial Advanced Technology Attachment (SATA), Integrated DriveElectronics (IDE), IEEE-1394, Universal Serial Bus (USB), fiber channel,Small Computer Systems Interface (SCSI), etc. The memory drives mayfurther include a drum, magnetic disc drive, magneto-optical drive,optical drive, Redundant Array of Independent Discs (RAID), solid-statememory devices, solid-state drives, etc.

The memory 1205 may store a collection of program or databasecomponents, including, without limitation, a user interface 1206, anoperating system 1207, a web browser 1208, and instructions 1215,etcetera. In various embodiments, instructions 1215 may includeinstructions that when executed by the processor 1202 cause theprocessor 1202 to perform one or more techniques, steps, procedures,and/or methods described herein, such to estimate a distance or performa calibration. For example, instructions to perform method 380 may bestored in memory 1205. In many embodiments, memory 1205 includes atleast one non-transitory computer-readable medium. In some embodiments,the computer system 1200 may store user/application data, such as thedata, variables, records, etc. as described in this disclosure. Suchdatabases may be implemented as fault-tolerant, relational, scalable,secure databases such as Oracle or Sybase.

The operating system 1207 may facilitate resource management andoperation of the computer system 1200. Examples of operating systemsinclude, without limitation, APPLE® MACINTOSH® OS X®, UNIX®, UNIX-likesystem distributions (E.G., BERKELEY SOFTWARE DISTRIBUTION® (BSD),FREEBSD®, NETBSD®, OPENBSD, etc.), LINUX® DISTRIBUTIONS (E.G., RED HAT®,UBUNTU®, KUBUNTU®, etc.), IBM®OS/2®, MICROSOFT® WINDOWS® (XP®,VISTA®/7/8, 10 etc.), APPLE® IOS®, GOOGLE™ ANDROID™, BLACKBERRY® OS, orthe like. The User interface 1206 may facilitate display, execution,interaction, manipulation, or operation of program components throughtextual or graphical facilities. For example, user interfaces mayprovide computer interaction interface elements on a display systemoperatively connected to the computer system 1200, such as cursors,icons, checkboxes, menus, scrollers, windows, widgets, etc. GraphicalUser Interfaces (GUIs) may be employed, including, without limitation,Apple® Macintosh® operating systems' Aqua®, IBM® OS/2®, Microsoft®Windows® (e.g., Aero, Metro, etc.), web interface libraries (e.g.,ActiveX®, Java®, JavaScript®, AJAX, HTML, Adobe® Flash®, etc.), or thelike.

In some embodiments, the computer system 1200 may implement the webbrowser 1208 stored program components. The web browser 1208 may be ahypertext viewing application, such as MICROSOFT® INTERNET EXPLORER®,GOOGLE™ CHROME™, MOZILLA® FIREFOX®, APPLE® SAFARI®, etc. Secure webbrowsing may be provided using Secure Hypertext Transport Protocol(HTTPS), Secure Sockets Layer (SSL), Transport Layer Security (TLS),etc. Web browsers 1208 may utilize facilities such as AJAX, DHTML,ADOBE® FLASH®, JAVASCRIPT®, JAVA®, Application Programming Interfaces(APIs), etc. In some embodiments, the computer system 1200 may implementa mail server stored program component. The mail server may be anInternet mail server such as Microsoft Exchange, or the like. The mailserver may utilize facilities such as Active Server Pages (ASP),ACTIVEX®, ANSI® C++/C#, MICROSOFT®, .NET, CGI SCRIPTS, JAVA®,JAVASCRIPT®, PERL®, PHP, PYTHON®, WEBOBJECTS®, etc. The mail server mayutilize communication protocols such as Internet Message Access Protocol(IMAP), Messaging Application Programming Interface (MAPI), MICROSOFT®exchange, Post Office Protocol (POP), Simple Mail Transfer Protocol(SMTP), or the like. In some embodiments, the computer system 1200 mayimplement a mail client stored program component. The mail client may bea mail viewing application, such as APPLE® MAIL, MICROSOFT® ENTOURAGE®,MICROSOFT® OUTLOOK®, MOZILLA® THUNDERBIRD®, etc.

Furthermore, one or more computer-readable storage media may be utilizedin implementing embodiments consistent with the present disclosure. Acomputer-readable storage medium refers to any type of physical memoryon which information or data readable by a processor may be stored.Thus, a computer-readable storage medium may store instructions forexecution by one or more processors, including instructions for causingthe processor(s) to perform steps or stages consistent with theembodiments described herein. The term “computer-readable medium” shouldbe understood to include tangible items and exclude carrier waves andtransient signals, i.e., non-transitory. Examples include Random AccessMemory (RAM), Read-Only Memory (ROM), volatile memory, non-volatilememory, hard drives, Compact Disc (CD) ROMs, Digital Video Disc (DVDs),flash drives, disks, and any other known physical storage media.

It will be understood by those within the art that, in general, termsused herein, and are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended. Forexample, as an aid to understanding, the detail description may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to disclosures containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations).

All of the devices and/or methods disclosed and claimed herein can bemade and executed without undue experimentation in light of the presentdisclosure. While the devices and methods of this disclosure have beendescribed in terms of preferred embodiments, it may be apparent to thoseof skill in the art that variations can be applied to the devices and/ormethods and in the steps or in the sequence of steps of the methoddescribed herein without departing from the concept, spirit, and scopeof the disclosure. All such similar substitutes and modificationsapparent to those skilled in the art are deemed to be within the spirit,scope and concept of the disclosure as defined by the appended claims.

What is claimed is:
 1. A system, comprising: a fiber laser; and acontroller comprising a processor and memory, the memory comprisinginstructions that when executed by the processor cause the processor to:determine a pulse energy for the fiber laser; identify a distancebetween a tip of the fiber laser and a target, wherein a liquid islocated between the tip of the fiber laser and the target; determine amodulation scheme based on the distance; set an initial pulse power forthe modulation scheme to generate an index bubble in the liquid based onthe distance; and initiate a pulse according to the modulation schemevia the fiber laser, wherein the modulation scheme reduces power of thepulse after initiation of the pulse at the initial pulse power.
 2. Thesystem of claim 1, wherein the modulation scheme increases power of thepulse to a maximal system power level at a time estimated for the indexbubble to reach maximal size.
 3. The system of claim 2, wherein theinstructions, when executed by the processor, further cause theprocessor to estimate the time the index bubble takes to reach maximalsize based on the initial pulse power and an absorption coefficient ofthe liquid at a wavelength of the fiber laser.
 4. The system of claim 1,wherein the instructions, when executed by the processor, further causethe processor to: identify an updated distance between the tip of thefiber laser and the target; and determine an updated modulation schemebased on the updated distance.
 5. The system of claim 1, wherein themodulation scheme is configured to modulate pulse power down duringexpansion of the index bubble and modulate pulse power up duringcollapse of the index bubble.
 6. The system of claim 1, wherein themodulation scheme comprises an initial modulation frequency and theinstructions, when executed by the processor, further cause theprocessor to determine the initial modulation frequency based on a timeto collapse of the index bubble, a time for the index bubble to reachmaximum size, and a time from lasing initiation to start of bubbleformation.
 7. The system of claim 1, wherein the instructions, whenexecuted by the processor, further cause the processor to set theinitial pulse power for the modulation scheme to generate the indexbubble in the liquid based on the distance and the pulse energy.
 8. Thesystem of claim 1, wherein the instructions, when executed by theprocessor, further cause the processor to integrate the power of thepulse with respect to time and terminate the pulse when the integral ofthe power of the pulse with respect to time equals the pulse energy. 9.The system of claim 1, wherein the instructions, when executed by theprocessor, further cause the processor to classify the target as distanttarget based on the distance and set the initial pulse power to amaximal system power level based on classification of the target asdistant.
 10. The system of claim 9, wherein the modulation scheme isconfigured obtain a resonant effect by cycling at periods between 0.7and 1.3 times a time from start to collapse of the index bubble.
 11. Atleast one non-transitory computer-readable medium comprising a set ofinstructions that, in response to being executed by a processor circuit,cause the processor circuit to: determine a pulse energy for a fiberlaser; identify a distance between a tip of the fiber laser and atarget, wherein a liquid is located between the tip of the fiber laserand the target; determine a modulation scheme based on the distance; setan initial pulse power for the modulation scheme to generate an indexbubble in the liquid based on the distance; and initiate a pulseaccording to the modulation scheme via the fiber laser, wherein themodulation scheme reduces power of the pulse after initiation of thepulse at the initial pulse power.
 12. The at least one non-transitorycomputer-readable medium of claim 11, wherein the modulation schemeincreases power of the pulse to a maximal system power level at a timeestimated for the index bubble to reach maximal size.
 13. The at leastone non-transitory computer-readable medium of claim 12, wherein the setof instructions, in response to execution by the processor circuit,further cause the processor circuit to estimate the time the indexbubble takes to reach maximal size based on the initial pulse power andan absorption coefficient of the liquid at a wavelength of the fiberlaser.
 14. The at least one non-transitory computer-readable medium ofclaim 11, wherein the set of instructions, in response to execution bythe processor circuit, further cause the processor circuit to: identifyan updated distance between the tip of the fiber laser and the target;and determine an updated modulation scheme based on the updateddistance.
 15. The at least one non-transitory computer-readable mediumof claim 11, wherein the set of instructions, in response to executionby the processor circuit, further cause the processor circuit to set theinitial pulse power for the modulation scheme to generate the indexbubble in the liquid based on the distance and the pulse energy.
 16. Theat least one non-transitory computer-readable medium of claim 11,wherein the set of instructions, in response to execution by theprocessor circuit, further cause the processor circuit to integrate thepower of the pulse with respect to time and terminate the pulse when theintegral of the power of the pulse with respect to time equals the pulseenergy.
 17. A method, comprising: determining a pulse energy for a fiberlaser; identifying a distance between a tip of the fiber laser and atarget, wherein a liquid is located between the tip of the fiber laserand the target; determining a modulation scheme based on the distance;setting an initial pulse power for the modulation scheme to generate anindex bubble in the liquid based on the distance; and initiating a pulseaccording to the modulation scheme via the fiber laser, wherein themodulation scheme reduces power of the pulse after initiation of thepulse at the initial pulse power.
 18. The method of claim 17, comprisingmodulating pulse power down during expansion of the index bubble andmodulating pulse power up during collapse of the index bubble.
 19. Themethod of claim 17, comprising classifying the target as distant targetbased on the distance and set the initial pulse power to a maximalsystem power level based on classification of the target as distant. 20.The method of claim 19, comprising cycling at periods between 0.7 and1.3 times a time from start to collapse of the index bubble.